With just a tiny bit of luck there is no need to pre-book your tickets - in most cases there are several seats left even an hour before the official starting time. Pre-ordering tickets does have an advantage though when it comes to prizing. One easy way to get your ticket it to book via Eventim.

If you happen to be younger than thirty consider buying yourself a Classic Card - it costs 15 Euros but allows you access to several locations for 8 Euros only (no pre-booking, tickets can be purchased only an hour before the official start).